* Two attacks since Sunday have killed 200 people
* Military offensive has not quelled Islamist violence
* Boko Haram fighting for Islamic state in north
By Ibrahim Mshelizza
BAMA, Nigeria, Feb 20 (Reuters) - Gunmen from Nigeria's Islamist Boko Haram sect killed 98 people in the northeastern town of Bama on Wednesday, residents there said after burying their folk, more than double the ...